The present application concerns picture and/or video coding and in particular codecs supporting block partitioning and skip mode.
Many picture and/or video codecs treat the pictures in units of blocks. For example, predictive codecs use a block granularity in order to achieve a good compromise between very precisely set prediction parameters set at a high spatial resolution with, however, spending too much side information for the prediction parameters on the one hand and too coarsely set prediction parameters, causing the amount of bits necessitated to encode the prediction residual to increase due to the lower spatial resolution of the prediction parameters, on the other hand. In effect, the optimum setting for the prediction parameters lies somewhere between both extremes.
Several attempts have been made in order to obtain the optimum solution for the above-outlined problem. For example, instead of using a regular subdivision of a picture into blocks regularly arranged in rows and columns, multi-tree partitioning subdivision seeks to increase the freedom of subdividing a picture into blocks at a reasonable demand for subdivision information. Nevertheless, even multi-tree subdivision necessitates the signalization of a remarkable amount of data and the freedom in subdividing a picture is quite restricted even in case of using such multi-tree subdivisioning.
In order to enable a better tradeoff between the amount of side information necessitated in order to signalize the picture subdivision on the one hand and the freedom in subdividing the picture on the other hand, merging of blocks may be used in order to increase the number of possible picture subdivisionings at a reasonable amount of additional data necessitated in order to signalize the merging information. For blocks being merged, the coding parameters need to be transmitted within the bitstream in full merely once, similarly as if the resulting merged group of blocks was a directly subdivided portion of the picture.
In order to additionally increase the efficiency in encoding the picture content, skip mode has been introduced into some block-based picture codecs, the skip mode enabling the encoder to refrain from transmitting the residual data of a certain block to the decoder. That is, the skip mode is a possibility to suppress residual data transmission for certain blocks. The ability to suppress the transmission of residual data for certain blocks results in a broader granularity interval for encoding the coding/prediction parameters within which an optimum tradeoff between coding quality on the one hand and total bit rate spent on the other hand may be expected: naturally, increasing the spatial resolution of the encoding of the coding/prediction parameters results in an increase of the side information rate while decreasing, however, the residuum thereby lowering the rate necessitated to encode the residual data. However, due to the availability of the skip mode, it may be favorable to obtain an abrupt coding rate saving by merely moderately further increasing the granularity at which the coding/prediction parameters are transmitted so that the residuum is so small that a separate transmission of the residuum may be left away.
However, there is still a need for achieving better coding efficiency, due to remaining redundancies newly caused by the combination of block merging and skip mode usage.